Technical Field
The present invention relates to a noise detection device that is based on computational fluid dynamics (CFD).
Related Art
Noise levels generated by a running vehicle are sometimes measured using microphone arrays installed in the ceiling and in the side walls of a wind tunnel laboratory, and microphones installed inside the vehicle cabin. However, because the microphone arrays installed respectively in the ceiling and the side walls are located at a distance from the surface of the vehicle providing the noise source, it has been difficult to precisely pinpoint the location of the noise source. Furthermore, in the microphones installed inside the vehicle cabin, the problem arises that the location of the source of wind noise from outside the vehicle is obstructed by the vehicle glass and the front pillars and, consequently, cannot be pinpointed.
Independently of the noise measurements carried out in a wind tunnel laboratory, noise levels generated by a running vehicle can also be calculated using CFD. In Japanese Patent Application Laid-Open (JP-A) No. 2013-134742 (Patent document 1), there is disclosed an invention relating to a method of predicting an aerodynamic noise level in which the pressure distribution on the surface of the side window glass of a vehicle model when the vehicle is running is calculated using CFD, and the level of the aerodynamic noise generated in the vicinity of the front pillars is predicted based on this pressure distribution.
The invention described in Patent document 1 predicts the level of aerodynamic noise generated in the vicinity of the front pillars, however, no consideration is given to predicting the aerodynamic noise level in any arbitrary location on the vehicle surface. Moreover, the invention described in Patent document 1 predicts the level of the aerodynamic noise generated in the vicinity of the front pillars based on the size of an area where the calculated negative pressure level exceeds a predetermined value, however, this invention still has the problem that it remains difficult to quantitatively calculate the strength of the source of the noise from the negative pressure level.
In CFD, it is comparatively easy to calculate what is known as the flow field. This is the calculation of the flow rate, density, and pressure of air, which is a fluid, on the surface of a vehicle model. Based on the calculation of the flow field, physical quantities such as pressure variations, the vorticity, and Lighthill's acoustic source isosurfaces and the like on the surface of that vehicle model can be calculated. However, although these physical properties are able to schematically show the trend of sound pressure changes in the noise from variations in the flow of the fluid, they do not enable the noise itself to be quantitatively calculated. Therefore, there is a concern that they are not suitable to be used to quantitatively evaluate the size of the noise.
Moreover, in CFD, in some cases, the aforementioned calculation of the flow field and the quantitative calculation of the noise are performed simultaneously. However, in order to perform these calculations, immense calculation resources and calculation times are required.